The present invention relates to thin loudspeakers, especially those that use multiple drivers to produce high fidelity sound.
A great deal of research has gone toward developing thin loudspeakers. Thin loudspeakers are in demand because they are less intrusive than conventional loudspeakers and hence can be utilized in a greater variety of ways.
Over the years, the design of thin loudspeakers has evolved. Early thin loudspeakers included a relatively stiff and substantially planar diaphragm mounted in a frame and coupled at its rear surface to a speaker voice coil. The voice coil would press the rear surface of the diaphragm and cause sufficient vibration of the diaphragm to produce sound.
Later thin loudspeakers incorporated piezoelectric elements as the driving elements. One of the first piezoelectric thin loudspeakers consisted of a vibrating film stretched on a frame with a plurality of piezoelectric drivers attached directly to the film. Although the use of piezoelectric driver elements allowed the loudspeakers to become more compact, the frequency responses of such systems were poor.
In order to improve the frequency response of thin loudspeakers, designers began to use different drivers to reproduce different segments of the audible spectrum. For example, U.S. Pat. No. 5,031,222 entitled Piezoelectric Speaker issued to Takaya discloses a flat panel loudspeaker that utilizes at least two groups of piezoelectric drivers which have different primary resonance frequencies. The primary resonance frequency of one group of piezoelectric drivers has a value between the primary resonance frequency and secondary resonance frequency of the other group. Likewise, U.S. Pat. No. 5,196,755 entitled Piezoelectric Panel Speaker issued to Shields discloses a planar loudspeaker that utilizes an array of piezoelectric elements. By including individual elements in the array with different resonance frequencies, the band of frequencies that can be reproduced is increased.
Despite the advances made in the area of thin loudspeakers, conventional thin loudspeakers still have limitations. None of the patents described above or any other reference disclose a loudspeaker that can provide a superior frequency response in a thin structure.
The present invention provides a thin loudspeaker that produces a superior frequency response and a diffuse acoustical pattern using magnetic drivers, acoustical plates, or a combination of magnetic drivers and acoustical plates. The invention contains a specially designed crossover network and a novel enclosure design. The novel enclosure includes a septum and cross bracing which enables the invention to realize superior performance in a thin loudspeaker design. The invention encompasses methods for improving the performance of an acoustical plate which include (1) placing acoustical plate motor elements on the plate in a manner that avoids rotational, mirror, and translational symmetry, (2) using acoustical plate motor elements of different shapes and sizes to stimulate the plate, and (3) using an acoustical plate that has an asymmetric shape. All of the embodiments of the invention may be covered with a decorative cover and hung on a wall like a picture or used to form a panel in a home entertainment center.
In a preferred embodiment, a plurality of acoustical plate motor elements are attached to an L-shaped acoustical plate secured above at least a portion of the thin loudspeaker""s septum. The acoustical plate motor elements are placed on the acoustical plate in a manner that avoids rotational, mirror, and translational symmetry. A magnetic driver is attached to the septum, and cross bracing connects the septum to the rear wall of the loudspeaker enclosure.
As pointed out in greater detail below, the present invention provides a thin loudspeaker that can reproduce high quality sound over a range of frequencies which was not previously possible in such a structure using a combination of magnetic drivers and acoustical plates.
It is an object of this invention to provide a thin loudspeaker that has the sensitivity of a conventional speaker and a diffuse acoustical radiation pattern.
It is another object of this invention to provide a thin loudspeaker that can efficiently provide a superior frequency response over the audible spectrum.
It is yet another object of this invention to create a thin loudspeaker that can provide superior acoustic performance utilizing either magnetic drivers, acoustical plates, or a combination of magnetic drivers and acoustical plates.